1 00:00:00,960 --> 00:00:09,119 In this video we are going to analyze how to solve the problems in which we have family trees 2 00:00:09,119 --> 00:00:16,160 representing the inheritance of a trait that is determined by a gene located in the sex chromosome 3 00:00:16,160 --> 00:00:24,480 in the x or in the y chromosome that are the pair 23. So the easiest thing is to analyze if this 4 00:00:24,480 --> 00:00:32,640 trait is y linked because the chromosome y is only present in men then analyze the squares 5 00:00:32,640 --> 00:00:47,219 the squares of the tree okay if there are only squares color in black this means that only men 6 00:00:47,219 --> 00:00:58,399 are affected by this disease or only men can have can show this trait and no circle is is color in 7 00:00:58,399 --> 00:01:07,799 black so there is no possibility of a woman showing this trait this means that the gene 8 00:01:07,799 --> 00:01:14,920 the trait that we are analyzing is located in the y chromosome this is the case okay you can see that 9 00:01:14,920 --> 00:01:26,900 All these squares are colored in black, all these squares are having the trait, but not the circles, no circles having the trait. 10 00:01:27,159 --> 00:01:37,379 There are some squares, like this individual that is 2-7, that is not showing the trait, but it's okay because he is from a different family. 11 00:01:37,379 --> 00:01:51,219 I mean, if you take this man that is having the trait because the square is colored in black, all his sons should also be colored in black, okay? 12 00:01:51,359 --> 00:01:58,299 But this guy is not a son of individual 1-4, so that is not a problem. 13 00:01:58,299 --> 00:02:01,099 for this man 14 00:02:01,099 --> 00:02:02,719 one one that is also 15 00:02:02,719 --> 00:02:05,120 coloring black that he is 16 00:02:05,120 --> 00:02:06,280 showing the trait 17 00:02:06,280 --> 00:02:08,840 he has only one son 18 00:02:08,840 --> 00:02:10,960 that is also coloring black 19 00:02:10,960 --> 00:02:12,960 so he also has the trait 20 00:02:12,960 --> 00:02:15,139 and this individual that is 21 00:02:15,139 --> 00:02:16,979 two two is 22 00:02:16,979 --> 00:02:19,000 having two sons 23 00:02:19,000 --> 00:02:21,340 that also are coloring black 24 00:02:21,340 --> 00:02:22,979 so everything fits 25 00:02:22,979 --> 00:02:25,080 this tree is representing 26 00:02:25,080 --> 00:02:27,460 the inheritance of a 27 00:02:27,460 --> 00:02:28,219 trait 28 00:02:28,300 --> 00:02:30,680 That is Y-linked. 29 00:02:31,180 --> 00:02:43,139 If woman, if any woman is affected, I mean, by the disease or is having the tree, then the trait is going to be X-linked. 30 00:02:43,139 --> 00:02:50,620 In this case, we can see circles that represent women that are colored in black. 31 00:02:50,979 --> 00:02:56,219 So this means that is an X-linked trait. 32 00:02:56,219 --> 00:03:05,159 Okay, now that we know that it's an X-linked trait, it can be both recessive or dominant. 33 00:03:07,000 --> 00:03:21,770 So, if the trait is recessive, all the sons of a woman, like this one, that has the trait that is colored in black, 34 00:03:21,770 --> 00:03:28,189 All the sons, man, are going also to show the trait. 35 00:03:28,930 --> 00:03:43,830 So all the squares, the men, that are sons from a woman that is coloring black, that has the trait, should be also coloring black. 36 00:03:43,830 --> 00:03:51,750 So the sons, boys, look at this individual 13 or individual 15. 37 00:03:52,370 --> 00:03:59,469 These boys that are sons of a woman with the trait also have the trait. 38 00:04:00,629 --> 00:04:03,430 And the same for five and seven. 39 00:04:03,669 --> 00:04:10,810 They are sons of a woman with the trait and they also have the trait. 40 00:04:10,810 --> 00:04:14,909 This means that the trait is recessive. 41 00:04:15,330 --> 00:04:27,209 If we have a woman that has the trait with a son that doesn't have the trait, then it should be dominant. 42 00:04:29,680 --> 00:04:30,600 This is the case. 43 00:04:30,600 --> 00:04:43,040 Over here, you have a woman with the trait that has one son also with the trait, but one son without the trait. 44 00:04:43,620 --> 00:04:49,360 This means that the trait should be X-linked and dominant. 45 00:04:49,959 --> 00:04:58,540 If it were recessive, both sons of this woman should show the trait. 46 00:04:58,540 --> 00:05:09,000 And for being sure that the trait is dominant, we are going to analyze the daughters of a man with the trait. 47 00:05:09,000 --> 00:05:23,339 Because if the disease or the trait is X-linked and it is dominant, a man that is having the disease is going to carry the X chromosome with the dominant allele. 48 00:05:23,339 --> 00:05:28,720 And this X chromosome is going to be netted by all his daughters. 49 00:05:29,300 --> 00:05:40,720 So if all the daughters, in this case 8 and 10, of a man, 7, that has the trait or the disease, 50 00:05:41,740 --> 00:05:48,720 they are going to also have the trait or the disease if this is dominant. 51 00:05:48,720 --> 00:06:04,939 OK, so for this type of exercises, you need to analyze the sons squares from a woman circle that has the trait. 52 00:06:04,939 --> 00:06:23,300 So you look for a black circle and analyze the squares that represent her sons and also the daughters, the circles of a man, a square that is also colored in black. 53 00:06:24,199 --> 00:06:33,939 Okay, so if all the sons of a woman with the trait have also the trait, it is going to be recessive. 54 00:06:33,939 --> 00:06:40,879 If the woman with the trait has at least one son without the trait, it is dominant. 55 00:06:41,360 --> 00:06:50,939 And the other way around, if all the daughters of a man with the trait also have the trait, it is going to be dominant. 56 00:06:51,439 --> 00:07:00,339 But if a man with the trait has at least one daughter without it, it is going to be recessive.